White bass can spawn with the right conditions (% higher than HSB but still low) where as HSB may be able to with one of the parentals (WB or SB) or HSB if the right conditions exist . Called functional sterility. See this from SRAC https://srac.tamu.edu/index.cfm/event/getFactSheet/whichfactsheet/54/
Hybrid striped bass, unlike some
other hybrids, is fertile. It is
oviparous (egg-laying) like the
parental species and produces eggs
and sperm in the spring when
temperatures are 15 to 20° C. Some
males mature at the age of 1 year
(approximately 250 mm long and 500
grams), and all are mature at 2 years
of age. A few females are mature at
2 years of age, but all are mature at 3
years. Females produce an average
of 160,000 eggs per pound of body
weight and spawn once a year.
Males may spawn many times over
the spawning season.
Natural spawning of hybrids has
been verified in a few instances.
They may participate in spawning
runs with striped bass or possibly
white bass. There are also confirmed
cases of reproduction in reservoirs
that contain only hybrid striped bass.
Hybrid striped bass produce sperm
and eggs during the spring when
water temperature is between 55 to
70° F. Temperatures of 65° to 68° F
are ideal for spawning hybrids and
the parental species. Spawning occurs
from mid-March through May
depending on location. Spawning
season in any one location usually
lasts 4 to 5 weeks. Hybrids have been
observed participating in spawning
acts in areas that contain clear shallow
rocky shoals that are 1 to 3 feet
deep. Females come to the surface
during the spawning act and several
males accompany her. The males appear
to bump and butt the female
which may stimulate egg release.
Released eggs are immediately fertilized
by the males.
The eggs of striped bass x white bass
hybrids are intermediate in size to
those of the parental species. They
are semi-buoyant like striped bass
eggs, although they seem to be
heavier than striped bass eggs. Eggs
of this cross are generally not adhesive
like white bass eggs and must
be buoyed up by the turbulent water
flow till they hatch. Other hybrid
crosses such as striped bass x white
perch have adhesive eggs.
Eggs hatch in approximately 2 days
at water temperatures of 65 to
68° F. At colder temperatures eggs
may take over 72 hours to hatch.
Newly hatched fry do not have fully
developed mouth parts and do not
feed until they are approximately 5
days old. During this swim-up stage
the relatively large oil droplet is used
as a food source.